Prior art object tracking systems are known in the art. Many prior art tracking systems use the Global Positioning System (GPS) to determine the three-dimensional position and velocity of an object. GPS is a network of 24 satellites and a dozen ground stations. Signals from four or more satellites are used to obtain the three-dimensional position and velocity of the object. GPS generally has a 100 meter ranging error for civil users and a 15 meter ranging error for military users, but these errors can be reduced by sophisticated error correction algorithms.
U.S. Pat. No. 5,438,518 describes a player positioning and distance finding system that uses GPS. The system includes a mobile interface unit that has a memory element, position interface electronics, a data processor, and a player interface. The memory element stores digitized map representations of playing fields. The position interface electronics receives position indicative signals that are representative of a geographical location of the mobile unit from the GPS. The data processor couples to the memory element and to the position interface electronics and correlates the geographical location to a field location of the mobile interface unit on the playing field. The processor also determines the distance from the mobile interface unit to a first landmark. The player interface is coupled to the data processor and communicates the distance between the mobile interface unit and the first landmark to the player.
Other tracking systems use a localized RF system. For example, U.S. Pat. No. 5,513,854 describes a process and a hardware system that allows real time automatic acquisition of a multitude of parameters which describe the physical activity of the athletes as well as a graphical representation of the parameters. Real time acquisition of the instantaneous position of every person on a game field is accomplished by use of a miniaturized radio frequency transmitter carried by the person and a set of at least three radio frequency goniometric receivers which determine the direction from which the transmitters transmit. A digital processor uses triangulation methods to determine the position of the transmitters.
U.S. Pat. No. 4,660,039 describes another tracking system that uses a localized RF system. This patent is directed to a system for locating a sport object. The user carries a radio frequency transmitter, and the sport object has a conductive stripe. The conductive strip has an effective length of one-quarter wavelengths at the signal frequency so that it increases the load on the transmitter as it moves closer to the sport object.
Several other RF tracking systems use coding techniques to identify the objects being tracked. For example, U.S. Pat. No. 5,056,106 describes a golf course ranging and direction-finding system that uses spread-spectrum radio location techniques. The system employs a spread-spectrum based radio location system to determine distance and direction between a golfer and key locations on a golf course. A plurality of timing reference transmitters are located throughout the vicinity of the golf course. The transmitters broadcast a spread-spectrum ranging signal consisting of a radio-frequency carrier directly modulated by a periodic pseudo-noise (PN) coded or similar sequence. Each transmitter broadcasts at the same RF signal but a unique PN-coded sequence is assigned to each transmitter. Golfers are provided with the hand-held receiving unit which receives the transmitter spread-spectrum signals and which synchronizes to the spread-spectrum signals in order to obtain range estimates to a selected set of reference transmitters.
U.S. Pat. No. 5,438,321 is directed to a location system for tracking miners underground. The system includes a number of identification stations connected to a central control station. Miners are issued portable identification modules which are fitted to their caplamps and are powered by their battery packs. The identification modules transmit unique identification signals that are received by the identification stations.
U.S. Pat. No. 5,450,070 is directed to an electronic missing file locator system that includes a transmitter to selectively transmit packets of radio frequency cycles indicative of the coded address of a particular folder. A transponder is attached to the folder and receives the transmission and responds thereto by producing an audible sound which enables the field to be easily located.
U.S. Pat. No. 5,458,123 is directed to a system for monitoring patient location and data. The system includes a transmitter associated with each patient that includes sensors operative to monitor vital signs of the patient. The transmitter transmits an allocated RF frequency which is particularly associated with that patient. A series of antennas are incorporated in a building, each antenna having its own signature signal. As the patient moves throughout the building, the antennas pick up the signals from the patient's transmitter and combines the antenna signature signal with the transmitted patient signal. This combined signal is then analyzed at a central location to determine the exact location of the patient due to the antenna signature signal which is modulated on the transmitted patient signal. Transmitted patient data is also decoded at the central station to provide a signal indicative of the vital signs of the patient.
U.S. Pat. No. 5,581,257 is directed to a radio frequency automatic identification system that detects targets. The system includes a plurality of radio frequency resonators. Information is attributed to the target in accordance with the radio frequency response characteristics of the target, such as the resonant frequencies of resonators present, and/or the spatial locations within the target of the resonators. Readers for use in the system read the radio frequency response characteristics of a target in the near field of a radiating aperture which is illuminated by a radio frequency source. Items which may be encoded with radio frequency readable information include documents, credit cards, and computer diskettes.
U.S. Pat. No. 5,583,517 is directed to a multi-path resistant frequency-hopped spread spectrum mobile location system. The frequency-hopped spread spectrum mobile vehicle or person location system consists of a central station, a plurality of base stations and a plurality of mobile transmitters which transmit using a frequency-hopped spread-spectrum differential bi-phase shift keying communication signal. Each of the plurality of base stations includes an array of receiving dipole antennas and employs a special algorithms for retrieving very low power frequency-hopped spread spectrum signals in a noisy and multi-path environment. The base stations use computational algorithms for determining the phase difference between each of the receiving dipole antennas to determine the direction of the transmitter relative to the location of the respective base station. The multiple directions of arrival angles of the received signal at each base station are corrected based on an n-dimensional ambiguity space to locate the most probable angles of arrival.
The prior art local area tracking systems have several limitations. For example, GPS based systems can not easily obtain centimeter accuracy. Also, GPS systems cannot be used indoors and may not work in urban or canyon environments. GPS and other prior art tracking systems have relatively slow update rates and, therefore, are not suitable for video application. Many prior art tracking systems require one or more highly precise clocks that are expensive and physically large. Also, many prior art tracking systems are not scaleable. In addition, prior art tracking systems do not employ transceivers capable of receiving instructions to transmit certain data at certain times.